1. Field of the Invention
The present invention relates to a fire sensor and a fire detecting method for detecting a fire using both sensor signals from a temperature sensor and a smoke sensor and, more particularly, a fire sensor and a fire detecting method for detecting a fire by correcting a smoke signal according to change in the temperature situation caused by the fire.
2. Description of the Related Art
Conventionally, as the multi-sensor type fire detecting method having both functions of detecting smoke and heat generated by the fire, there is the fire detecting method set forth in U.S. Pat. No. 5,005,003.
According to the multi-sensor type fire detecting method, in the situation that the heat generated by the fire is detected by a temperature sensor and then a detected temperature is increased in excess of a certain level, a smoke detection sensitivity can be increased by lowering a threshold value, by which the fire is decided based on a smoke signal being detected by the smoke sensor, to thus detect early the fire. In contrast, if the temperature detected by the temperature sensor is less than another certain level, the smoke detection sensitivity can be decreased by increasing the threshold value of the smoke sensor to thus prevent a false alarm. However, according to the method in which the detection sensitivity for the smoke signal supplied from the smoke sensor is changed based on the detected temperature by the temperature sensor, if the temperature is increased although its temperature rise is caused gradually, e.g., if a room temperature is increased in the summer season, if a temperature is increased by the heating or the like, the detection sensitivity of the smoke sensor is increased. Therefore, the smoke, the steam, etc. other than the fire are judged erroneously as the fire, and hence it may be a cause of the non-fire alarm.
In the fire detecting method using the temperature sensor, there is a method utilizing a differential element which can detect a rate of temperature rise relative to the time and then decide the fire based on the rapid temperature rise. According to the fire detecting method utilizing the differential element, because the smoke detection sensitivity is decreased at the time of the slow temperature rise whereas the smoke detection sensitivity is increased at the time of the quick temperature rise, the fire can be detected without fail even if a smoke density is low. However, in the fire detecting method utilizing the differential element, if the hot air of the heating, etc. blows directly against the fire sensor irrespective of the low room temperature, the smoke detection sensitivity is increased due to the rapid temperature rise. Therefore, the smoke generated by the causes other than the fire is judged as the fire, and hence it may be also a cause of the non-fire alarm.